[pulseaudio-discuss] redirecting audio from SAA7134 tv card

Luca DELLA GHEZZA luca_dgh at hotmail.it
Fri Oct 2 12:54:57 PDT 2009

On vie, 2009-10-02 at 10:11 +0200, Lennart Poettering wrote:
> On Thu, 01.10.09 12:38, Luca DELLA GHEZZA (luca_dgh at hotmail.it) wrote:
> > I can ear the tv audio from the standard output. That is fantastic,
> > because I tried as well with the BT headset and it works.
> > 
> > Sadly the audio has a very poor quality:
> > 1) the audio is pulsing, it seems that it pump up and down the master
> > volume
> Uh? You say the volume changes all the time? That is weird. Maybe this
> is due to reception quality?

it is not correct to say that the volume changes, it is more correct to
say that that the volume pump up and down always at the same levels and
with the same time interval.
I don't believe it is due to the reception quality because if I use sox
to redirect the tv audio the volume is not pumping.

> Does this alos happen if you use this loopback stuff for your webcam mic?

I tried to use loopback to redirect the webcam mic directly to standard
output and there is no volume pumping.

> 2) the rate is wrong, because it seems an old 33 rpm listening at
> > 45.
> Hmm, that is interesting. We actually resample the stream as necessary
> to deal with clock deviations between the sink and the source. On
> crappy devices where the timing interfcae is broken that might cause
> some weird effects. Now for the SAxxx TV drivers it is a fact that the
> driver is crappy. For example, it already chokes when we skip
> configuration of a hw buffers size/period size.
> Normally, the rate should stabilize after a while even on crappy
> devices. You might be able to improve behaviour by playing around with
> "adjust_time" (increase it to 30 or so...)

I tried to use the adjust_time but is not working, I tried:
as well I changed 3 to 0 or other values, but no ways.
The default should be 10 seconds, but I waited for one minute and
nothing has changed.

> > When I use sox to redirect audio it needs to set the rate to 32000, but
> > in this case has no effect.
> > I use s16le format because I know that the format used from the tv card
> > is Signed Little Endian 16 bit.
> > Finally I tried to change the latency to 1 and as well to 2000 but
> > nothing change, or very little changes.
> Yes, this is simply a hint. If the underlying devices cannot do this
> the actual measured latency might deviate substantially, both upwards
> and downwards. This is expected.
> > I need different settings or may be I need to change the sink
> > device?
> Normally, you shouldn't need any settings.
> Lennart

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